When an image displayed on a monitor of a computer system or the like is to be printed out from a printer, a so-called color matching process is generally required which performs adjustment so that the appearance of printed colors substantially equals the appearance of monitor display colors, since the color reproduction region of a monitor largely differs from that of a printer. A known example of this color matching process is a method of looking up a color correction table which is formed by taking account of the color characteristics of a monitor and a printer.
After this color matching process is executed, the user sometimes determines, on the basis of the image printed by a printer, that a specific color and its nearby colors further require fine adjustment. This fine adjustment is performed by changing the values of the above-mentioned color correction table for color matching, or by changing the values of individual pixels of the image data.
If, however, only a specific color is changed in a pinpoint manner in order to perform fine adjustment as in the above conventional method, density discontinuation occurs particularly in gradation images.
To prevent this problem, there is an adjustment method where a masking coefficient is calculated in such a way that a specific color becomes a desired color, and colors distant from the specific color change only slightly. Using the calculated coefficient, a masking process is performed for all values in the color correction table (or for all pixel values in image data). This method does not cause any density discontinuation as described above. With this method, however, it is difficult to limit the range over which the adjustment has its effect. The method also requires a long processing time.